Method and apparatus for spinal stabilization

ABSTRACT

A method and apparatus of limiting at least one degree of movement between a superior vertebrae and an inferior vertebrae of a patient includes advancing a distal end of a stabilization device into a pedicle of the inferior vertebrae. A proximal portion of the stabilization device is positioned such that the proximal portion limits at least one degree of movement between a superior vertebrae and an inferior vertebrae by contacting a surface of the superior vertebrae.

PRIORITY INFORMATION

This application is a continuation of U.S. patent application Ser. No.13/035,889, filed Feb. 25, 2011, is a continuation of U.S. patentapplication Ser. No. 11/296,881, filed Dec. 8, 2005, which is acontinuation-in-part of U.S. patent application Ser. No. 11/185,442,filed Jul. 20, 2005, which is a continuation-in-part of U.S. patentapplication Ser. No. 11/056,991, filed Feb. 11, 2005, which claims thepriority benefit under 35 U.S.C. § 119(e) of Provisional Application60/634,203 filed Dec. 8, 2004, the disclosures of each are incorporatedby reference herein in their entireties.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to medical devices and, more particularly,to methods and apparatuses for spinal stabilization.

Description of the Related Art

The human spine is a flexible weight bearing column formed from aplurality of bones called vertebrae. There are thirty three vertebrae,which can be grouped into one of five regions (cervical, thoracic,lumbar, sacral, and coccygeal). Moving down the spine, there aregenerally seven cervical vertebra, twelve thoracic vertebra, five lumbarvertebra, five sacral vertebra, and four coccygeal vertebra. Thevertebra of the cervical, thoracic, and lumbar regions of the spine aretypically separate throughout the life of an individual. In contrast,the vertebra of the sacral and coccygeal regions in an adult are fusedto form two bones, the five sacral vertebra which form the sacrum andthe four coccygeal vertebra which form the coccyx.

In general, each vertebra contains an anterior, solid segment or bodyand a posterior segment or arch. The arch is generally formed of twopedicles and two laminae, supporting seven processes—four articular, twotransverse, and one spinous. There are exceptions to these generalcharacteristics of a vertebra. For example, the first cervical vertebra(atlas vertebra) has neither a body nor spinous process. In addition,the second cervical vertebra (axis vertebra) has an odontoid process,which is a strong, prominent process, shaped like a tooth, risingperpendicularly from the upper surface of the body of the axis vertebra.Further details regarding the construction of the spine may be found insuch common references as Gray's Anatomy, Crown Publishers, Inc., 1977,pp. 33-54, which is herein incorporated by reference.

The human vertebrae and associated connective elements are subjected toa variety of diseases and conditions which cause pain and disability.Among these diseases and conditions are spondylosis, spondylolisthesis,vertebral instability, spinal stenosis and degenerated, herniated, ordegenerated and herniated intervertebral discs. Additionally, thevertebrae and associated connective elements are subject to injuries,including fractures and torn ligaments and surgical manipulations,including laminectomies.

The pain and disability related to the diseases and conditions oftenresult from the displacement of all or part of a vertebra from theremainder of the vertebral column. Over the past two decades, a varietyof methods have been developed to restore the displaced vertebra totheir normal position and to fix them within the vertebral column.Spinal fusion is one such method. In spinal fusion, one or more of thevertebra of the spine are united together (“fused”) so that motion nolonger occurs between them. The vertebra may be united with varioustypes of fixation systems. These fixation systems may include a varietyof longitudinal elements such as rods or plates that span two or morevertebrae and are affixed to the vertebrae by various fixation elementssuch as wires, staples, and screws (often inserted through the pediclesof the vertebrae). These systems may be affixed to either the posterioror the anterior side of the spine. In other applications, one or morebone screws may be inserted through adjacent vertebrae to providestabilization.

Although spinal fusion is a highly documented and proven form oftreatment in many patients, there is currently a great interest insurgical techniques that provide stabilization of the spine whileallowing for some degree of movement. In this manner, the natural motionof the spine can be preserved, especially for those patients with mildor moderate disc conditions. In certain types of these techniques,flexible materials are used as fixation rods to stabilize the spinewhile permitting a limited degree of movement.

Notwithstanding the variety of efforts in the prior art described above,these techniques are associated with a variety of disadvantages. Inparticular, these techniques typically involve an open surgicalprocedure, which results higher cost, lengthy in-patient hospital staysand the pain associated with open procedures.

Therefore, there remains a need for improved techniques and systems forstabilization the spine. Preferably, the devices are implantable througha minimally invasive procedure.

SUMMARY OF THE INVENTION

Accordingly, one embodiment of the present invention comprises a methodlimiting extension between an inferior and superior body structure of aspine. The method comprises inserting a stabilization into a patientfrom a lateral or anterior site and coupling a stabilization device onlyto the inferior body structure of the spine such that a portion of thestabilization device limits extension between the superior bodystructure and the inferior body structure.

Another embodiment of the present invention also comprises a method oflimiting at least one degree of movement a superior vertebrae and aninferior vertebrae of a patient. The method comprises providing acomplementary interface on the superior adjacent vertebrae and advancinga distal end of a stabilization device into the inferior vertebrae;positioning a proximal portion of the stabilization device such that theproximal portion abuts against the complementary interface to limit atleast one degree of movement between the superior vertebrae and theinferior vertebrae.

Another embodiment of the present invention comprises a spinalstabilization device that includes an elongate body, having a proximalend and a distal end, a distal anchor on the distal end of the elongatebody and a proximal anchor carried to the body and having an outersurface that is radially adjustable with respect to the elongated body.

Another embodiment of the present invention comprises a spinalstabilization device that includes a body, having a proximal end and adistal end, a distal anchor on the distal end of the elongate body, aretention structure on the body, proximal to the distal anchor, and aproximal anchor, carried by the body, and having a diameter, theproximal anchor having means for adjusting the diameter of the proximalanchor.

Yet another embodiment of the present invention comprises a kit forspinal stabilization that comprises a spinal stabilization device andinstructions for coupling the stabilization device only to an inferiorbody structure of the spine such that a portion of the stabilizationdevice limits extension between the superior body structure and theinferior body structure.

Another embodiment of the present invention comprises a kit for spinalstabilization that includes a spinal stabilization device comprising adistal end and a proximal end and instructions for inserting the distalend into an inferior vertebral body and positioning the proximal end ofthe device such that the device limits extension between the inferiorvertebrae and a superior vertebrae body by contacting a surface of thesuperior vertebrae or an intermediate member coupled to the superiorvertebrae.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A a side elevational view of a portion of a vertebra having anexemplary embodiment of a stabilization device implanted therein.

FIG. 1B is a posterior view of a portion of a vertebra having twodevices similar to that of FIG. 1A implanted substantially bilaterallytherein.

FIG. 1C is a posterior view of a portion of a vertebra having twodevices similar to that of FIG. 1A implanted substantially bilaterallytherein and a member extending between the two devices.

FIG. 2 is a side perspective view of the stabilization device of FIGS.1A and 1B.

FIG. 3 is a side view of the stabilization device of FIG. 2.

FIG. 3A is a cross-sectional view of a body portion of the stabilizationdevice of FIG. 2.

FIG. 4 is a partial cross-sectional view of a proximal portion of thestabilization device of FIG. 2.

FIG. 5 is an enlarged view of a portion of FIG. 4 labeled 5-5.

FIG. 6 is a side perspective view of a locking ring of the stabilizationdevice of FIG. 3.

FIG. 7 is a side view of a modified embodiment of a body portion of thestabilization device shown in FIG. 2.

FIG. 7A is an enlarged view of a portion of FIG. 7 labeled 7A-7A.

FIG. 8 is a posterior view of a portion of a vertebra portions thereofremoved to receive a fixation device.

FIG. 9A is a side view of a device configured to remove portions of avertebra.

FIG. 9B is a enlarged side view of the distal end of the device of FIG.9A.

FIG. 9C is a side view of a tool configured to insert a body of astabilization device.

FIG. 9D is an enlarged side view of the tool of FIG. 9C.

FIG. 9E is an enlarged side view of the tool of FIG. 9C with a body of astabilization device inserted therein.

FIG. 10A is a side view of another embodiment of a stabilization device.

FIG. 10B is a cross-sectional side view of the stabilization device ofFIG. 10A.

FIGS. 11A and 11B are perspective rear and front views of anotherembodiment of a proximal anchor.

FIGS. 12A and 12B are perspective rear and front views of anotherembodiment of a proximal anchor.

FIGS. 13A and 13B are perspective rear and front views of anotherembodiment of a proximal anchor.

FIG. 14 is a side view of another modified embodiment of the proximalanchor.

FIG. 15 is a side perspective view of another modified embodiment of theproximal anchor.

FIG. 16 is a side view of another modified embodiment of the proximalanchor.

FIG. 17 is a side perspective view of an embodiment of an insertion toolconfigured to insert a proximal onto a body portion of a fixationdevice.

FIG. 18 is a cross-sectional side view of the insertion tool of FIG. 17.

FIG. 19 is a cross-sectional side view of a modified embodiment of astabilization device.

FIG. 20A is a cross-sectional side view of a modified embodiment of astabilization device in a un-expanded configuration.

FIG. 20B is a cross-sectional side view of a modified embodiment of astabilization device in an expanded configuration.

FIG. 20C is a closer cross-sectional side view of the embodiment of FIG.20A in a un-expanded configuration.

FIG. 20D is a closer cross-sectional side view of the embodiment of FIG.20B in an expanded configuration

FIG. 21 is a cross-sectional side view of a modified embodiment of astabilization device in an expanded configuration.

FIG. 22 is a cross-sectional side view of another modified embodiment ofa stabilization device in an expanded configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the stabilization devices of the present invention will bedisclosed primarily in the context of a spinal stabilization procedure,the methods and structures disclosed herein are intended for applicationin any of a variety medical applications, as will be apparent to thoseof skill in the art in view of the disclosure herein. For example,certain features and aspects of bone stabilization device and techniquesdescribed herein may be applicable to proximal fractures of the femurand a wide variety of fractures and osteotomies, the hand, such asinterphalangeal and metacarpophalangeal arthrodesis, transversephalangeal and metacarpal fracture fixation, spiral phalangeal andmetacarpal fracture fixation, oblique phalangeal and metacarpal fracturefixation, intercondylar phalangeal and metacarpal fracture fixation,phalangeal and metacarpal osteotomy fixation as well as others known inthe art. See e.g., U.S. Pat. No. 6,511,481, which is hereby incorporatedby reference herein. A wide variety of phalangeal and metatarsalosteotomies and fractures of the foot may also be stabilized using thebone fixation devices described herein. These include, among others,distal metaphyseal osteotomies such as those described by Austin andReverdin-Laird, base wedge osteotomies, oblique diaphyseal, digitalarthrodesis as well as a wide variety of others that will be known tothose of skill in the art. Fractures of the fibular and tibial malleoli,pilon fractures and other fractures of the bones of the leg may befixated and stabilized with these bone fixation devices with or withoutthe use of plates, both absorbable or non-absorbing types, and withalternate embodiments of the current invention The stabilization devicesmay also be used to attach tissue or structure to the bone, such as inligament reattachment and other soft tissue attachment procedures.Plates and washers, with or without tissue spikes for soft tissueattachment, and other implants may also be attached to bone, usingeither resorbable or nonresorbable fixation devices depending upon theimplant and procedure. The stabilization devices may also be used toattach sutures to the bone, such as in any of a variety of tissuesuspension procedures. The bone stabilization device described hereinmay be used with or without plate(s) or washer(s), all of which can beeither permanent, absorbable, or combinations.

FIGS. 1A and 1B are side and rear elevational views of a pair of bonestabilization devices 12, positioned within a body structure 10 a of thespine. As will be explained in detail below, the bone stabilizationdevice 12 may be used in a variety of techniques to stabilize the spine.In one embodiment, the device 12 is attached (e.g., inserted or screwedinto) and/or coupled to a single body structure and limits motion of asecond body structure. In the another embodiment, the device 12 limitsextension in the spine by being attached and/or coupled to an inferiorbody structure and limiting motion of an adjacent superior bodystructure. “Body structure” as used herein is the anterior solid segmentand the posterior segment of any vertebrae of the five regions(cervical, thoracic, lumbar, sacral, and coccygeal) of the spine. Insome embodiments, the device limits motion by contacting, abuttingagainst and/or wedging against the adjacent body structure and/or adevice coupled to the adjacent body structure.

With reference to the illustrated embodiment of FIGS. 1A and 1B, thedistal end of the bone stabilization device 12 is inserted into thepedicle of the inferior vertebrae, preferably through the pars (i.e.,the region between the lamina between and the superior articularprocesses). The proximal end of the device 12 extends above the parssuch that it limits motion of a superior adjacent vertebrae 10 b withrespect to the inferior adjacent vertebrae 10 b. In one embodiment, theproximal end of the device limits motion by abutting and/or wedgingagainst a surface of the superior adjacent vertebrae as the superioradjacent vertebrae moves relative to the inferior adjacent vertebrae. Inthis manner, at least one degree of motion between the inferior andsuperior vertebrae may be limited. For example, the spine generally hassix (6) degrees of motion which include flexion, extension, left andright lateral bending and axial rotation or torsion. In the illustratedembodiment, at least extension of the spine is limited. Embodiments inwhich the devices are inserted with bilateral symmetry can be used tolimit left and right lateral bending.

In the illustrated embodiment, motion of the spine is limited when theproximal end of the device contacts, abuts, and/or wedges against theinferior articular process of the superior adjacent vertebra 10 b. Inthis application, it should be appreciated that one or more intermediatemember(s) (e.g., plates, platforms, coatings, cement, and/or adhesives)can be can be coupled to the superior adjacent vertebra 10 b or otherportions of the spine that the device contacts, abuts, and/or wedgesagainst. Thus, in this application, when reference is made to the devicecontacting, abutting and/or wedging against a portion of the spine itshould be appreciated that this includes embodiments in which the devicecontacts, abuts and/or wedges against one or more intermediate membersthat are coupled to the spine unless otherwise noted.

As explained below, the bone stabilization devices 12 may be used afterlaminectomy, discectomy, artificial disc replacement, microdiscectomy,laminotomy and other applications for providing temporary or permanentstability in the spinal column. For example, lateral or central spinalstenosis may be treated with the bone fixation devices 12 and techniquesdescribed below. In such procedures, the bone fixation devices 12 andtechniques may be used alone or in combination with laminectomy,discectomy, artificial disc replacement, and/or other applications forrelieving pain and/or providing stability.

An embodiment of the stabilization device 12 will now be described indetail with initial reference to FIGS. 2-4. The stabilization device 12comprises a body 28 that extends between a proximal end 30 and a distalend 32. The length, diameter and construction materials of the body 28can be varied, depending upon the intended clinical application. Inembodiments optimized for spinal stabilization in an adult humanpopulation, the body 28 will generally be within the range of from about20-90 mm in length and within the range of from about 3.0-8.5 mm inmaximum diameter. The length of the helical anchor, discussed below, maybe about 8-80 millimeters. Of course, it is understood that thesedimensions are illustrative and that they may be varied as required fora particular patient or procedure.

In one embodiment, the body 28 comprises titanium. However, as will bedescribed in more detail below, other metals, or bioabsorbable ornonabsorbable polymeric materials may be utilized, depending upon thedimensions and desired structural integrity of the finishedstabilization device 12.

The distal end 32 of the body 28 is provided with a cancellous boneanchor and/or distal cortical bone anchor 34. Generally, for spinalstabilization, the distal bone anchor 34 is adapted to be rotationallyinserted into a portion (e.g., the pars or pedicle) of a first vertebra.In the illustrated embodiment, the distal anchor 34 comprises a helicallocking structure 72 for engaging cancellous and/or distal corticalbone. In the illustrated embodiment, the locking structure 72 comprisesa flange that is wrapped around a central core 73, which in theillustrated embodiment is generally cylindrical in shape. The flange 72extends through at least one and generally from about two to about 50 ormore full revolutions depending upon the axial length of the distalanchor 34 and intended application. The flange will generally completefrom about 2 to about 60 revolutions. The helical flange 72 ispreferably provided with a pitch and an axial spacing to optimize theretention force within cancellous bone. While the helical lockingstructure 72 is generally preferred for the distal anchor, it should beappreciated that other distal anchor could comprises other structuresconfigured to secure the device in the cancellous bone anchor and/ordistal cortical bone, such as, for example, various combinations andsub-combinations of hooks, prongs, expandable flanges, etc. See alsoe.g., U.S. Pat. No. 6,648,890, the entirety of which is herebyincorporated by reference herein.

The helical flange 72 of the illustrated embodiment has a generallytriangular cross-sectional shape (see FIG. 3A). However, it should beappreciated that the helical flange 72 can have any of a variety ofcross sectional shapes, such as rectangular, oval or other as deemeddesirable for a particular application through routine experimentationin view of the disclosure herein. For example, in one modifiedembodiment, the flange 72 has a triangular cross-sectional shape with ablunted or square apex. One particularly advantageous cross-sectionalshape of the flange are the blunted or square type shapes. Such shapescan reduce cutting into the bone as the proximal end of the device isactivated against causing a windshield wiper effect that can loosen thedevice 12. The outer edge of the helical flange 72 defines an outerboundary. The ratio of the diameter of the outer boundary to thediameter of the central core 73 can be optimized with respect to thedesired retention force within the cancellous bone and giving dueconsideration to the structural integrity and strength of the distalanchor 34. Another aspect of the distal anchor 34 that can be optimizedis the shape of the outer boundary and the central core 73, which in theillustrated embodiment are generally cylindrical.

The distal end 32 and/or the outer edges of the helical flange 72 may beatraumatic (e.g., blunt or soft). This inhibits the tendency of thestabilization device 12 to migrate anatomically distally and potentiallyout of the vertebrae after implantation. Distal migration is alsoinhibited by the dimensions and presence of a proximal anchor 50, whichwill be described below. In the spinal column, distal migration isparticularly disadvantageous because the distal anchor 34 may harm thetissue, nerves, blood vessels and/or spinal cord which lie within and/orsurround the spine. Such features also reduce the tendency of the distalanchor to cut into the bone during the “window-wiper effect” that iscaused by cyclic loading of the device as will be described. In otherembodiments, the distal end 32 and/or the outer edges of the helicalflange 72 may be sharp and/or configured such that the distal anchor 34is self tapping and/or self drilling.

A variety of other embodiments for the distal anchor 32 can also beused. For example, the various distal anchors described in co-pendingU.S. patent application Ser. No. 10/012,687, filed Nov. 13, 2001 can beincorporated into the stabilization device 12 described herein. Theentire contents of this application are hereby expressly incorporated byreference. In particular, the distal anchor 32 may comprise a singlehelical thread surrounding a lumen, much as in a conventional corkscrew.Alternatively, a double helical thread may be utilized, with the distalend of the first thread rotationally offset from the distal end of thesecond thread. The use of a double helical thread can enable a greateraxial travel for a given degree of rotation and greater retention forcethan a corresponding single helical thread. Specific distal anchordesigns can be optimized for the intended use, taking into accountdesired performance characteristics, the integrity of the distal bone,and whether the distal anchor is intended to engage exclusivelycancellous bone or will also engage cortical bone. In still otherembodiments, the distal anchor 34 may be formed without a helicalflange. For example, various embodiments of levers, prongs, hooks and/orradially expandable devices may also be used. See e.g., U.S. Pat. No.6,648,890, which is hereby expressly incorporated by reference in itsentirety.

As shown in FIG. 3A, the body 28 is cannulated forming a central lumen42 to accommodate installation over a placement wire as is understood inthe art. The cross section of the illustrated central lumen is circularbut in other embodiments may be non circular, e.g., hexagonal, toaccommodate a corresponding male tool for installation or removal of thebody 28 as explained below. In other embodiments, the body 28 maypartially or wholly solid.

With continued reference to FIGS. 2-4, the proximal end 30 of the body28 is provided with a rotational coupling 70, for allowing the body 28to be rotated. Rotation of the rotational coupling 70 can be utilized torotationally drive the distal anchor 32 into the bone. In suchembodiments, any of a variety of rotation devices may be utilized, suchas electric drills or hand tools, which allow the clinician to manuallyrotate the proximal end 30 of the body 28. Thus, the rotational coupling70 may have any of a variety of cross sectional configurations, such asone or more curved faces, flats or splines. In the illustratedembodiment, the rotational coupling 70 is a male element in the form ofa hexagonal projection. However, in other embodiments, the rotationalcoupling 70 may be in the form of a female component, machined, milledor attached to the proximal end 30 of the body 28. For example, in onesuch embodiment, the rotational coupling 70 comprises an axial recesswith a polygonal cross section, such as a hexagonal cross section. Asexplained above, the axial recess may be provided as part of the centrallumen 42.

The proximal end 30 of the fixation device is also provided with aproximal anchor 50. The proximal anchor 50 comprises a housing 52, whichforms a lumen 53 (see FIG. 5) configured such that the body 28 mayextend, at least partially, through the proximal anchor 50. The proximalanchor 50 is axially distally moveable along the body 28 such that theproximal anchor 50 can be properly placed with respect the inferiorvertebral and superior vertebra. As will be explained below,complimentary locking structures such as threads, levers, split rings,and/or ratchet like structures between the proximal anchor 50 and thebody 28 resist proximal movement of the anchor 50 with respect to thebody 28 under normal use conditions. The proximal anchor 50 preferablycan be axially advanced along the body 28 with and/or without rotationas will be apparent from the disclosure herein.

With particular reference to FIGS. 4-6, in the illustrated embodiment,the complementary structure of the proximal anchor 50 is formed by anannular ring 51, which is positioned within an annular recess 55 formedalong the lumen 53. As will be explained below, the ring 51 comprisessurface structures 54 which interact with complimentary surfacestructures 58 on the body 28. In the illustrated embodiment, thecomplimentary surface structures 58 comprise a series of annular ridgesor grooves 60 formed on the surface of the body 28. The surfacestructures 54 and complementary surface structures 58 permit distalaxial travel of the proximal anchor 50 with respect to the body 28, butresist proximal travel of the proximal anchor 50 with respect to thebody 28 as explained below.

As shown in FIG. 6, the annular ring 51 is split (i.e., has a least onegap) and is interposed between the body 28 and the recess 55 of theproximal anchor 50 (see FIG. 5). In the illustrated embodiment, the ring51 comprises a tubular housing 57 (see FIG. 6), which defines a gap orspace 59. In one embodiment, the gap 59 is defined by a pair of edges 61a, 61 b, that are generally straight and parallel to each other.Although not illustrated, it should be appreciated that in modifiedembodiments, the ring 51 can be formed without a gap. When the ring 51is positioned along the body 28, the ring 51 preferably surrounds asubstantial portion of the body 28. The ring 51 can be configured sothat the ring 51 can flex or move radially outwardly in response to anaxial force so that the ring 51 can be moved relative to the body 28, asdescribed below.

In the illustrated embodiment, the tubular housing 57 includes at leastone and in the illustrated embodiment ten teeth or flanges 63, which areconfigured to engage the complementary surface structures 58 on the body28 in a ratchet-like motion. In the illustrated embodiment (see FIG. 5),the teeth or flanges include a first surface 65 that lies generallyperpendicular to the longitudinal axis of the anchor and generally facesthe proximal direction (i.e., the direction labeled “P” in FIG. 5) and asecond surface 67 that is inclined with respect to the longitudinal axisof the anchor and that faces distal direction (i.e., the directionlabeled “D” in FIG. 5). It should be noted that the proximal anddirections in FIG. 5 are reversed with respect to FIG. 4.

With continued reference to FIG. 5, the recess 55 is sized anddimensioned such that as the proximal anchor 50 is advanced distallyover the body, the second surface 67 of the annular ring 51 can slidealong and over the complementary retention structures 58 of the body 28.That is, the recess 55 provides a space for the annular ring to moveradially away from the body 28 as the proximal anchor 50 is advanceddistally.

A distal portion 69 of the recess 55 is sized and dimensioned such thatafter the proximal anchor 50 is appropriately advanced, proximal motionof the proximal anchor 50 is resisted as the annular ring 51 becomeswedged between the body 28 and an angled engagement surface 71 of thedistal portion 69. In this manner, proximal movement of the proximalanchor 50 under normal use conditions may be prevented. In modifiedembodiments, the annular ring 51 can be sized and dimensioned such thatthe ring 51 is biased inwardly to engage the retention structures 58 onthe body 28. The bias of the annular ring 51 can result in a moreeffective engagement between the complementary retention structures 58of the body and the retention structures 54 of the ring 51.

In certain embodiments, it is advantageous for the outer surface 49 ofthe proximal anchor 50 to rotate with respect to the body 28. Thisarrangement advantageously reduces the tendency of the body 28 to rotateand/or move within the superior articular process of the inferiorvertebrae 10 a as the outer surface 49 contacts, abuts or wedges againstthe inferior articular process of the superior vertebrae 10 b. In theillustrated embodiment, rotation of the outer surface 49 is provided byconfiguring the lumen 53 and annular recess 55 such that the anchor 50can rotate about the body 28 and ring 51. Preferably, as the anchor 50rotates the axial position of the anchor 50 with respect to the body 28remains fixed. That is, the annular ring 51 resists proximal travel ofthe proximal anchor 50 with respect to the body 28 while the anchor 50is permitted to rotate about the body 28 and ring 51. Of course those ofskill in the art will recognize other configurations and mechanisms(e.g., bearings, rollers, slip rings, etc.) for providing rotation ofthe outer surface 49 with respect to the body 28. In a modifiedembodiment, the proximal anchor 50 can be configured such that it doesnot rotate with respect to the body 28. In such an embodiment, a key orone or more anti-rotational features (e.g., splines, grooves, flatsides, etc.) can be provided between the proximal anchor 50, the ring 51and/or the body 51 to limit or prevent rotation of the proximal anchor50 with respect to the body 28.

As mentioned above, it is contemplated that various other retentionstructures 54 and complementary retention structures 58 may be usedbetween the body 28 and the proximal anchor 50 to permit distal axialtravel of the proximal anchor 50 with respect to the body 28, but resistproximal travel of the proximal anchor 50 with respect to the body 28.Examples of such structures can be found in U.S. Pat. No. 6,685,706,entitled “PROXIMAL ANCHORS FOR BONE FIXATION SYSTEM.” The entirecontents of this patent is hereby expressly incorporated by referenceherein. In such embodiments, the structures 54 and complementaryretention structures 58 can be configured to allow the proximal anchorto be advanced with or without rotation with respect to the body 28.

As mentioned above, the complimentary surface structures 58 on the body28 comprise threads, and/or a series of annular ridges or grooves 60.These retention structures 58 are spaced axially apart along the body28, between a proximal limit 62 and a distal limit 64. See FIG. 4. Theaxial distance between proximal limit 62 and distal limit 64 is relatedto the desired axial working range of the proximal anchor 50, and thusthe range of functional sizes of the stabilization device 12. Thus, thestabilization device 12 of the example embodiment can provide accurateplacement between the distal anchor 34 and the proximal anchor 50throughout a range of motion following the placement of the distalanchor in a vertebra. That is, the distal anchor 34 may be positionedwithin the cancellous and/or distal cortical bone of a vertebra, and theproximal anchor may be distally advanced with respect to the distalanchor throughout a range to provide accurate placement of the proximalanchor 50 with respect to the vertebra without needing to relocate thedistal anchor 34 and without needing to initially locate the distalanchor 34 in a precise position with respect to the proximal side of thebone or another vertebra. The arrangement also allows the compressionbetween the distal anchor 34 and the proximal anchor 50 to be adjusted.Providing a working range throughout which positioning of the proximalanchor 50 is independent from setting the distal anchor 34 allows asingle device to be useful for a wide variety of different anatomies, aswell as eliminates or reduces the need for accurate device measurement.In addition, this arrangement allows the clinician to adjust thecompression force during the procedure without adjusting the position ofthe distal anchor. In this manner, the clinician may focus onpositioning the distal anchor sufficiently within the vertebra to avoidor reduce the potential for distal migration out of the vertebra, whichmay damage the particularly delicate tissue, blood vessels, nervesand/or spinal cord surrounding or within the spinal column. In additionor alternative, the above described arrangement allows the clinician toadjust the positioning of the proximal anchor 50 with respect to theinferior articular process of the superior adjacent vertebrae. In thismanner, the clinician may adjust the position of the proximal anchor 50without adjusting the position of the distal anchor such that the anchor50 is configured to wedge or abut against inferior articular process ofthe superior adjacent vertebrae. In a modified embodiment, the positionof the proximal anchor 50 with respect to the surrounding vertebra canbe adjusted by rotating the device 12 and advancing the distal anchorand the proximal anchor carried by the body.

In the embodiment of FIGS. 4-6, the proximal anchor 50 can be distallyadvanced over the body 28 without rotating the proximal anchor 50 withrespect to the body 28. In one embodiment, the ring 51 and the proximalanchor 50 are rotationally linked by, for example, providinginter-engaging structures (e.g., tabs, ridges and the like). In such anembodiment, the proximal anchor 50 can be advanced without rotating theproximal anchor 50 and be removed and/or the position adjusted in aproximal or distal direction by rotating the proximal anchor withrespect to the body 28. This can allow the surgeon to remove an proximalanchor and use a different sized or configured proximal anchor 50 if thefirst proximal anchor is determined to be inadequate. In such anembodiment, the proximal anchor 50 is preferably provided with one ormore engagement structures (e.g., slots, hexes, recesses, protrusions,etc.) configured to engage a rotational and/or gripping device (e.g.,slots, hexes, recesses, protrusions, etc.). Thus, in some embodiments,the proximal anchor 50 can be pulled and/or rotated such that the anchor50 is removed from the body.

In many applications, the working range is at least about 10% of theoverall length of the device, and may be as much as 20% or 50% or moreof the overall device length. In the context of a spinal application,working ranges of up to about 10 mm or more may be provided, sinceestimates within that range can normally be readily accomplished withinthe clinical setting. The embodiments disclosed herein can be scaled tohave a greater or a lesser working range, as will be apparent to thoseof skill in the art in view of the disclosure herein.

In embodiments optimized for spinal stabilization in an adult humanpopulation, the anchor 50 will have a diameter within the range of fromabout 1 to 1/16 of an inch in another embodiment the proximal anchorproximal anchor 50 within the range from about 0.5 to ⅛ of an inch inanother embodiment.

With reference back to FIGS. 2-4, in the illustrated embodiment, theouter surface 49 of the proximal anchor 50 has a smooth or sphericalshape. As will be explained below, the outer surface 49 of the proximalanchor 50 is configured to abut against the inferior facet of thesuperior adjacent vertebrae. In this manner, motion between the adjacentvertebrae may be limited and/or constrained.

FIG. 7 illustrates an embodiment in which the body 28 comprises a firstportion 36 and a second portion 38 that are coupled together at ajunction 40. In the illustrated embodiment, the first portion 36 carriesthe distal anchor 34 (shown without a central core) while the secondportion 38 forms the proximal end 30 of the body 28. As will beexplained in more detail below, in certain embodiments, the secondportion 38 may be used to pull the body 28 and therefore will sometimesbe referred to as a “pull-pin.” The first and second portions 36, 38 arepreferably detachably coupled to each other at the junction 40. In theillustrated embodiment, the first and second portions 36, 38 aredetachably coupled to each other via interlocking threads. Specifically,as best seen in FIG. 7A, the body 28 includes an inner surface 41, whichdefines a central lumen 42 that preferably extends from the proximal end30 to the distal end 32 throughout the body 28. At the proximal end ofthe first portion 36, the inner surface 41 includes a first threadedportion 44. The first threaded portion 44 is configured to mate with asecond threaded portion 46, which is located on the outer surface 45 ofthe second portion 38. The interlocking annular threads of the first andsecond threaded portions 44, 46 allow the first and second portions 36,38 to be detachably coupled to each other. In one modified embodiment,the orientation of the first and second threaded portions 44, 46 can bereversed. That is, the first threaded portion 44 can be located on theouter surface of the first portion 36 and the second threaded portion 46can be located on the inner surface 41 at the distal end of the secondportion 38. Any of a variety of other releasable complementaryengagement structures may also be used, to allow removal of secondportion 38 following implantation, as is discussed below.

In a modified arrangement, the second portion 38 can comprise any of avariety of tensioning elements for permitting proximal tension to beplaced on the distal anchor 34 while the proximal anchor is advanceddistally to compress the fracture. For example, any of a variety oftubes or wires can be removably attached to the first portion 36 andextend proximally to the proximal handpiece. In one such arrangement,the first portion 36 can include a releasable connector in the form of alatching element, such as an eye or hook. The second portion 38 caninclude a complementary releasable connector (e.g., a complementaryhook) for engaging the first portion 36. In this manner, the secondportion 38 can be detachably coupled to the first portion 36 suchproximal traction can be applied to the first portion 36 through thesecond portion as will be explained below. Alternatively, the secondportion 48 may be provided with an eye or hook, or transverse bar,around which or through which a suture or wire may be advanced, bothends of which are retained at the proximal end of the device. Followingproximal tension on the tensioning element during the compression and/orpositioning step, one end of the suture or wire is released, and theother end may be pulled free of the device. Alternate releasableproximal tensioning structures may be devised by those of skill in theart in view of the disclosure herein.

In a final position, the distal end of the proximal anchor 50 preferablyextends distally past the junction 40 between the first portion 36 andthe second portion 38. As explained above, the proximal anchor 50 isprovided with one or more surface structures 54 for cooperating withcomplementary surface structures 58 on the first portion 36 of the body28.

In this embodiment, the stabilization device 12 may include anantirotation lock (not shown) between the first portion 36 of the body28 and the proximal collar 50. For example, the first portion 36 mayinclude one or more of flat sides (not shown), which interact withcorresponding flat structures in the proximal collar 50. As such,rotation of the proximal collar 50 is transmitted to the first portion36 and distal anchor 34 of the body 28. Of course, those of skill in theart will recognize various other types of splines or other interfitstructures can be used to prevent relative rotation of the proximalanchor and the first portion 36 of the body 28. To rotate the proximalanchor 50, the housing 52 may be provided with a gripping structure (notshown) to permit an insertion tool to rotate the flange proximal anchor50. Any of a variety of gripping structures may be provided, such as oneor more slots, recesses, protrusions, flats, bores or the like. In oneembodiment, the proximal end of the proximal anchor 50 is provided witha polygonal, and, in particular, a pentagonal or hexagonal recess orprotrusion.

Methods implanting stabilization devices described above as part of aspinal stabilization procedure will now be described. Although certainaspects and features of the methods and instruments described herein canbe utilized in an open surgical procedure, the disclosed methods andinstruments are optimized in the context of a percutaneous or minimallyinvasive approach in which the procedure is done through one or morepercutaneous small openings. Thus, the method steps which follow andthose disclosed are intended for use in a trans-tissue approach.However, to simplify the illustrations, the soft tissue adjacent thetreatment site have not been illustrated in the drawings.

In one embodiment of use, a patient with a spinal instability isidentified. The patient is preferably positioned face down on anoperating table, placing the spinal column into a normal or flexedposition. A trocar optionally may then be inserted through a tissuetract and advanced towards a first vertebrae. In another embodiment,biopsy needle (e.g., Jamshidi™) device can be used. A guidewire may thenbe advanced through the trocar (or directly through the tissue, forexample, in an open surgical procedure) and into the first vertebrae.The guide wire is preferably inserted into the pedicle of the vertebraepreferably through the pars (i.e. the region of the lamina between thesuperior and inferior articular processes). A suitable expandable accesssheath or dilator can then be inserted over the guidewire and expandedto enlarge the tissue tract and provide an access lumen for performingthe methods described below in a minimally invasive manner. In amodified embodiment, a suitable tissue expander (e.g., a balloonexpanded catheter or a series of radially enlarged sheaths) can beinserted over the guidewire and expanded to enlarge the tissue tract. Asurgical sheath can then be advanced over the expanded tissue expander.The tissue expander can then be removed such that the surgical sheathprovides an enlarged access lumen. Any of a variety of expandable accesssheaths or tissue expanders can be used, such as, for example, a balloonexpanded catheter, a series of radially enlarged sheaths inserted overeach other, and/or the dilation introducer described in U.S. patentapplication Ser. No. 11/038,784, filed Jan. 19, 2005 (Publication No.2005/0256525), the entirety of which is hereby incorporated by referenceherein.

A drill with a rotatable tip may be advanced over the guidewire andthrough the sheath. The drill may be used to drill an opening in thevertebrae. The opening may be configured for (i) for insertion of thebody 28 of the bone stabilization device 12, (ii) taping and/or (iii)providing a counter sink for the proximal anchor 50. In otherembodiments, the step of drilling may be omitted. In such embodiments,the distal anchor 34 is preferably self-tapping and self drilling. Inembodiments, in which an opening is formed, a wire or other instrumentmay be inserted into the opening and used to measure the desired lengthof the body 29 of the device 12.

The body 28 of the fixation device may be advanced over the guidewireand through the sheath until it engages the vertebrae. The body 28 maybe coupled to a suitable insertion tool prior to the step of engagingthe fixation device 12 with the vertebrae. The insertion tool may beconfigured to engage the coupling 70 on the proximal end of the body 28such that insertion tool may be used to rotate the body 28. In such anembodiment, the fixation device 12 is preferably configured such that itcan also be advanced over the guidewire.

The insertion tool may be used to rotate the body 28 thereby driving thedistal anchor 34 to the desired depth within the pedicle of thevertebrae. The proximal anchor 50 may be carried by the fixation deviceprior to advancing the body 28 into the vertebrae, or may be attachedand/or coupled to the body 28 following placement (partially or fully)of the body 28 within the vertebrae. In another embodiment, the anchor50 may be pre-attached and/or coupled to the body 28.

In one embodiment, the clinician will have access to an array of devices12, having, for example, different diameters, axial lengths,configurations and/or shapes. The clinician will assess the position ofthe body 28 with respect to the superior vertebrae and chose the device12 from the array, which best fits the patient anatomy to achieve thedesired clinical result. In another embodiment, the clinician will haveaccess to an array of devices 12, having, for example, bodies 28 ofdifferent diameters, axial lengths. The clinician will also have anarray of proximal anchors 50, having, for example, differentconfigurations and/or shapes. The clinician will choose the appropriatebody 28 and then assess the position of the body 28 with respect to thesuperior vertebrae and chose the proximal anchor 50 from the array,which best fits the patient anatomy to achieve the desired clinicalresult. In such an embodiment, the proximal anchor 50 is advantageouslycoupled to body 28 after the body 28 is partially or fully inserted intothe vertebrae.

Once the distal anchor 34 is in the desired location, the proximalanchor 50 is preferably advanced over the body 28 until it reaches itsdesired position. This may be accomplished by pushing on the proximalanchor 50 or by applying a distal force to the proximal anchor 50. Inanother embodiment, the proximal anchor 50 is advanced by applying aproximal retraction force to the proximal end 30 of body 28, such as byconventional hemostats, pliers or a calibrated loading device, whiledistal force is applied to the proximal anchor 50. In this manner, theproximal anchor 50 is advanced distally with respect to the body 28until the proximal anchor 50 is in its proper position (e.g., positionedsnugly against the outer surface of the vertebra.) Appropriatetensioning of the stabilization device 12 can be accomplished by tactilefeedback or through the use of a calibration device for applying apredetermined load on the stabilization device 12. As explained above,one advantage of the structure of the illustrated embodiments is theability to adjust the compression and/or the position of the proximalanchor 50 independently of the setting of the distal anchor 34 withinthe vertebra. For example, the positioning of the distal anchor 34within the vertebra can be decoupled from the positioning of theproximal anchor 50 with respect to the superior vertebra.

In one embodiment, the proximal anchor 50 is pushed over the body 28 bytapping the device with a slap hammer or similar device that can be usedover a guidewire. In this manner, the distal end of the device 12 isadvantageously minimally disturbed, which prevents (or minimizes) thethreads in the bore from being stripped.

Following appropriate tensioning of the proximal anchor 50, the proximalportion of the body 28 extending proximally from the proximal anchor 50can be removed. In one embodiment, this may involve cutting the proximalend of the body 28. For example, the proximal end of the body may beseparated by a cutting instrument or by cauterizing. Cauterizing mayfuse the proximal anchor 50 to the body 32 thereby adding to theretention force between the proximal anchor 50 and the body 28. Suchfusion between the proximal anchor and the body may be particularlyadvantageous if the pin and the proximal anchor are made from apolymeric or plastic material. In this manner, as the material of theproximal anchor and/or the pin is absorbed or degrades, the fusioncaused by the cauterizing continues to provide retention force betweenthe proximal anchor and the body. In another embodiment, the bodycomprises a first and a second portion 36, 38 as described above. Insuch an embodiment, the second portion 38 may detached from the firstportion 36 and removed. In the illustrated embodiment, this involvesrotating the second portion 38 with respect to the first portion via thecoupling 70. In still other embodiments, the proximal end of the body 28may remain attached to the body 28.

The access site may be closed and dressed in accordance withconventional wound closure techniques and the steps described above maybe repeated on the other side of the vertebrae for substantial bilateralsymmetry as shown in FIGS. 1A and 1B. The bone stabilization devices 12may be used alone or in combination with other surgical procedures suchas laminectomy, discectomy, artificial disc replacement, and/or otherapplications for relieving pain and/or providing stability.

As will be explained below, the superior body structure (e.g., superiorvertebrae the superior vertebrae 10 b) can be conformed to the device byproviding a complementary surface or interface. In one embodiment, thesuperior vertebrae can be modified using a separate drill or reamer thatis also used to from the countersink 300 described above. In otherembodiments, the drill that is used to form an opening in the inferiorsuperior body can be provided with a countersink portion that is alsoused to modify the shape of the superior vertebrae 10 b. In still otherembodiments, the shape of the superior vertebrae 10 b can be modifiedusing files, burrs and other bone cutting or resurfacing devices to froma complementary surface or interface for the proximal anchor 50.

As mentioned above, a countersink can be provided for the proximalanchor 50. With reference to FIG. 8, a pair of counter sinks 300 areshown formed in or near the pars of the inferior vertebrae 10 a. Eachcounter sink 300 is preferably configured to generally correspond to adistal facing portion 49 a (see FIG. 4 or FIG. 10A) of the proximalanchor 50. In this manner, the proximal anchor 50, in a final position,may be seated at least partially within the inferior vertebrae 10 a. Inthe illustrated embodiment, the countersink 300 has a generallyspherical configuration that corresponds generally to the sphericalshape of the distal portion 49 a of the proximal anchor 50 of theillustrated embodiment. In modified embodiments, the countersink 300 canhave a modified shape (e.g., generally cylindrical, conical,rectangular, etc.) and/or generally configured to correspond to thedistal portion of a proximal anchor 50 with a different shape than theproximal anchor illustrated in FIGS. 2-4.

The countersink 300 advantageously disperses the forces received by theproximal anchor 50 by the superior vertebrae 10 b and transmits saidforces to the inferior vertebrae 10 a. As will be explained in moredetail below, the countersink 300 can be formed by a separate drillinginstrument or by providing a counter sink portion on a surgical drillused to from a opening in the body 10 b.

In addition or in the alternative to creating the countersink 300, theshape of the inferior articular process IAP (which can include the facetin certain embodiments) of the superior vertebrae 10 b may be modifiedin order to also disperse the forces generated by the proximal anchor 50contacting, abutting and/or wedging against the superior vertebrae 10 b.For example, as shown in FIG. 8, a portion 304 of the inferior articularprocess IAP of the superior vertebrae 10 b that generally faces theproximal anchor 50 can be removed with the goal of dispersing and/orreducing the forces applied to the proximal anchor 50. In theillustrated embodiment, the inferior articular process is provided witha generally rounded recess 306 that corresponds generally to the roundedouter surface 49 of the proximal anchor 50. In modified embodiments, theinferior articular process IAP can be formed into other shapes in lightof the general goal to reduce and/or disperse the forces applied to theproximal anchor 50 For example, in certain embodiments, the inferiorarticular process IAP may be formed into a generally flat, blunt orcurved shape. In other embodiments, the inferior articular process IAPmay be configured to abut and/or wedge more efficiently with a proximalanchor 50 of a different shape (e.g., square, oval, etc.). In general,the countersink 300 and surface 306 provided for an increased contactsurface between the superior vertebra and the proximal anchor 50 and theinferior vertebra and the proximal anchor 50. This contact area reducesstress risers in the device and the associated contact areas of thevertebrae. In addition, the windshield wiper affect is reduced as theforces transmitted to the proximal anchor 50 from the superior vertebraeare transmitted through the area formed by the countersink 300.

FIGS. 9A and 9B illustrate an exemplary embodiment of a device 310 thatcan be used to form the countersink 300 and/or the recess 306 describedabove. As shown, the device comprises a body 312 having a distal end314, a proximal end 316 an a guidewire lumen (not shown) extendingtherethrough. The proximal end 316 is configured to engage any of avariety of standard driving tools as is known in the art. The distal end314 is provided with an outer surface 320 that generally corresponds tothe outer surface 49 of the proximal anchor 50. The outer surface 320 isalso provided with one or more removal or cutting features 318 (e.g.,flutes, sharp edges, etc.) so as to remove or cut bone as the device 310is rotated. A pin 321 (shown in dashed lines in FIG. 9B) can be providedat the end of the device 310. The pin 321 can be inserted into the holeformed in the vertebrae and helps to center and support the device 321at it cuts the countersink 300 and/or recess 306 into the bone.

In use, the device 310 is advanced over a guidewire that is insertedinto the inferior vertebrae 10 b. As the device 310 is advanced androtated, the device 310 encounters the inferior process IAP (see FIG. 8)of the superior vertebrae 10 b and portions thereof are removed. Furtheradvancement of the device 310, forms the countersink 300 in the superiorprocess of the inferior vertebrae 10 a and removes additional portionsof the superior vertebrae 10 b. Accordingly, in this embodiment, thedevice 310 can be used to form both the countersink 300 and to changethe shape of the inferior articular process IAP of the superiorvertebrae 10 b.

FIGS. 9C-E illustrate an insertion tool 600 that may be used to rotateand insert the body 29 as described above. As shown, the tool 600generally comprises an elongated shaft 602 having a distal end 604, aproximal end 606 and a guidewire lumen 608 extending there through. Inthe illustrated embodiment, the proximal end 604 includes a flat edge610 and engagement feature 612 for engaging a driving tool (e.g., adrill). In modified embodiments, the proximal end 606 can include ahandle such that the tool 600 can be rotated manually.

The distal end 604 of the tool 606 is provided with an distal sleeveportion 614 which has an outer shape that preferably correspondssubstantially to the outer surface shape of the proximal anchor used inthe procedure. Within the distal sleeve portion 614 is a lumen 616,which communicates with the guidewire lumen 608 and is configured toreceive the proximal end of the body 28. The lumen 616 includes arotational region 618 configured to engage the coupling 70 on theproximal end of the body 28. Distal to the rotational region 618 is arecess 620 in which an elastic or resilient member 622 (e.g., a siliconsleeve) can be placed. As shown in FIG. 9E, when the proximal end of thebody 28 is inserted into the lumen 616, the rotational region 618engages the coupling 70 and the elastic or resilient member 622 gripsthe body 28 to hold the body 28 in place within the tool 600.

As described above, the insertion tool 600 may be used to rotate thebody 28 thereby driving the distal anchor 34 to the desired depth withinthe pedicle of the vertebrae. The surgeon can stop rotating the body 28before the distal end of the tool 600 contacts the bone. In embodiments,in which a countersink is formed, the tool 600 can be rotated until thedistal end sits within the countersink at which point further rotationof the tool 600 will not cause the distal anchor to advance further asfurther advancement of the body 28 causes it to be released from thetool 600. In this manner, over advancement of the distal anchor 32 intothe vertebrae can be prevented or limited.

It should be appreciated that not all of the steps described above arecritical to procedure. Accordingly, some of the described steps may beomitted or performed in an order different from that disclosed. Further,additional steps may be contemplated by those skilled in the art in viewof the disclosure herein, without departing from the scope of thepresent invention.

With reference to FIGS. 1A and 1B, the proximal anchors 50 of thedevices 12 extend above the pars such that they abut against theinferior facet of the superior adjacent vertebrae. In this manner, theproximal anchor 50 forms a wedge between the vertebra limitingcompression and/or extension of the spine as the facet of the superioradjacent vertebrae abuts against the proximal anchor 50. In this manner,extension is limited while other motion is not. For example, flexion,lateral movement and/or torsion between the superior and inferiorvertebra is not limited or constrained. In this manner, the naturalmotion of the spine can be preserved, especially for those patients withmild or moderate disc conditions. Preferably, the devices areimplantable through a minimally invasive procedure and, more preferably,through the use of small percutaneous openings as described above. Inthis manner, the high cost, lengthy in-patient hospital stays and thepain associated with open procedures can be avoided and/or reduced. Inone embodiment, the devices 12 may be removed and/or proximal anchors 50may be removed in a subsequent procedure if the patient's conditionimproves. Once implanted, it should be appreciated that, depending uponthe clinical situation, the proximal anchor 50 may be positioned suchthat it contacts surfaces of the adjacent vertebrae all of the time,most of the time or only when movement between the adjacent vertebraeexceeds a limit.

In some instances, the practitioner may decide to use a more aggressivespinal fixation or fusion procedure after an initial period of using thestabilization device 12. In one particular embodiment, the bonestabilization device 12 or a portion thereof may be used as part of thespinal fixation or fusion procedure. In one such application, theproximal anchor 50 can be removed from the body 28. The body 28 canremain in the spine and used to support a portion of a spinal fixationdevice. For example, the body 28 may be used to support a fixation rodthat is coupled to a device implanted in a superior or inferiorvertebrae. Examples of such fusion systems can be found in U.S. patentapplication Ser. No. 10/623,193, filed Jul. 18, 2003, the entirety ofwhich is hereby incorporated by reference herein.

As mentioned above, in certain embodiments described above, it may beadvantageous to allow the proximal anchor to rotate with respect to thebody 28 thereby preventing the proximal anchor 50 from causing thedistal anchor 34 from backing out of the pedicle. In another embodiment,engagement features (as described below) may be added to the proximalanchor 50 to prevent rotation of the proximal anchor 50.

FIG. 1C illustrates a modified embodiment in which the first and secondfixation devices 12 a, 12 b are coupled together by a member 5 thatextends generally around or above the spinous process of the superiorvertebra 10 b. In this manner, the member 5 can be used to limit flexionof the spinal column. The member may comprise an of a variety ofsuitable structural members. In one embodiment, the member comprises asuture or wire that is tied to the proximal end of the bodies 28 or theproximal anchor. In certain embodiments, various hooks or eyelets can beprovided on the body or proximal anchor to facilitate coupling themember to the devices 12 a, 12 b.

The fixation devices 12 described herein may be made from conventionalnon-absorbable, biocompatible materials including stainless steel,titanium, alloys thereof, polymers, composites and the like andequivalents thereof. In one embodiment, the distal anchor comprises ametal helix, while the body and the proximal anchor comprise abioabsorbable material. Alternatively, the distal anchor comprises abioabsorbable material, and the body and proximal anchor comprise eithera bioabsorbable material or a non-absorbable material.

In one embodiment, the proximal anchor 50 is formed, at least in part,from an elastic and/or resilient material. In this manner, the shock andforces that are generated as the proximal anchor abuts or wedges againstthe inferior articular process of the superior adjacent vertebrae can bereduced or dissipated. In one such embodiment, the proximal anchor 50 isformed in part by a polycarbonate urethane or a hydrogel. In suchembodiments, the elastic material may be positioned on the outersurfaces of the proximal anchor or the portions of the outer surfacesthat abut against the surfaces of the inferior articular process of thesuperior adjacent vertebrae. In one embodiment, such an anchor has anelastic modules that is lower than metal (e.g, titanium). In anotherembodiment, the elastic modules is substantially close to that of bone).In yet another embodiment, the elastic modules is less than bone. Inthis manner, the stress risers generated during cyclic loading can bereduce reducing the tendency of the inferior articular process and theinferior vertebrae to crack during cyclic loading.

For example, FIGS. 10A and 10B illustrates an embodiment of device 12′with a proximal anchor 50′ that comprises an outer housing or shell 202.The shell 202 may be formed or a resilient material such as, forexample, a biocompatible polymer. The proximal anchor 50′ also comprisesan inner member 204 that comprises a tubular housing 206 and a proximalflange 208. The inner member 202 is preferably formed of a harder morerugged material as compared to the shell 202, such as, for example,titanium or another metallic material. The shell 202 is fitted or formedover the tubular housing 206. When deployed, the shell 202 is held inplace between the flange 208 and the surface of the vertebrae in whichthe body 202 is placed. In modified embodiments, the shell 202 may becoupled to the inner member 204 in a variety of other manners, such as,adhesives, fasteners, interlocking surfaces structures and the like. Inthe illustrated embodiment, the inner member 204 includes a locking ring51 positioned within a recess 55 as described above. Of course, inmodified embodiments, other retention structures 54 and complementaryretention structures 58 may be used between the body 28 and the proximalanchor 50′ to permit distal axial travel of the proximal anchor 50′ withrespect to the body 28, but resist proximal travel of the proximalanchor 50′ with respect to the body 28.

In the illustrated embodiment of FIGS. 10A and 10B, the distal anchor 34is provided with atraumatic or blunt tip 7. In addition, the flange 72of the distal anchor 34 includes a square or blunt edges. These featuresreduce the tendency of the distal anchor to cut into the bone during thewindow-wiper effect that is caused by cyclic loading of the device asdescribed above.

In another embodiment, the proximal anchor 50 is provided with amechanically resilient structure. Thus, as with the previous embodiment,the shock and forces that are generated as the proximal anchor abuts orwedges against the inferior articular process of the superior adjacentvertebrae can be reduced or dissipated. In one such embodiment, theproximal anchor 50 is provided with mechanical springs, lever armsand/or the like. In such embodiments, as the mechanically resilientstructure is compressed or extended the shock and forces are reduced ordissipated.

For example, FIGS. 11A-13B. illustrate embodiments of a proximal anchor400, which comprises a tubular housing 402, which includes a recess 403for receiving a locking ring 51 as described above. The distal end 404of the housing 402 forms a generally rounded, semi-spherical face thatcan be inserted into a corresponding counter sink 300 (see FIG. 8) asdescribe above. Extending from the housings 402 are a plurality of leverarms or deflectable flanges 410. Each arm 410 generally comprises agenerally radially extending portion 412 and a generally circumferentialextending portion 414. In the illustrated embodiments, two (FIGS.13A-B), three (FIGS. 12A-B) and five arms (FIGS. 11A-B) are shown.However, the anchor 400 can include different numbers of arms (e.g.,one, four or greater than five arms). As the superior adjacent vertebrae10 b moves against the proximal anchor 400 the radially extendingportion 414 deflects relative to the tubular housing 402 to absorb ordisperse the forces generated by the contact.

As mentioned above, in the illustrated embodiment, the tubular member402 includes a locking ring 51 positioned within a recess 403 asdescribed above. Of course, in modified embodiments, other retentionstructures and complementary retention structures may be used betweenthe body 28 and the proximal anchor 400 to permit distal axial travel ofthe proximal anchor 400 with respect to the body 28, but resist proximaltravel of the proximal anchor 400 with respect to the body 28.

With reference to FIG. 14, in a modified embodiment, the distal end ofthe proximal anchor 50 may include one or more bone engagement features100, which in the illustrated embodiment comprises a one or more spikes102 positioned on a contacting surface 104 of the proximal anchors. Thespikes 102 provide additional gripping support especially when theproximal anchor 50 is positioned against, for example, uneven bonesurfaces and/or soft tissue. In addition, the spikes 102 may limitrotation of the proximal anchor 50 with respect to the body 28 therebypreventing the proximal anchor 50 from backing off the body 28. Otherstructures for the bone engagement feature 100 may also be used, suchas, for example, ridges, serrations etc.

FIGS. 15 and 16 illustrate modified shapes of the proximal anchor whichcan be used alone or in combination with the elastic or resilientmaterial described above. In FIG. 15, the proximal anchor 250 has asaddle shaped curved surface 251 that generally faces the inferiorarticular process of the superior adjacent vertebrae. In thisembodiment, the saddle shaped surface may limit compression and/orextension of the adjacent vertebra and limit side to side motion and/ortorsion between the vertebra. FIG. 16 illustrates an embodiment in whichthe proximal anchor 350 has a rectangular shape with a flat shapedsurface 351. In this embodiment, the flat shaped surface may limitcompression and/or extension of the adjacent vertebra and limit side toside motion between the vertebra. In the embodiments of FIGS. 15 and 16,in may be advantageous to limit or eliminate any rotation of theproximal anchor 50 with respect to the body 28 and/or the vertebrae. Assuch, the proximal anchor 50 preferably includes the retention devices100 described above with reference to FIG. 14.

As mentioned above, in certain embodiments, clinician will also have anarray of proximal anchors 50, having, for example, differentconfigurations and/or shapes. The clinician will choose the appropriatebody 28 and then assess the position of the body 28 with respect to thesuperior vertebrae and chose the proximal anchor 50 from the array,which best fits the patient anatomy to achieve the desired clinicalresult. In such an embodiment, the proximal anchor 50 is advantageouslycoupled to body 28 after the body 28 is partially or fully inserted intothe vertebrae. The clinician may also be provided with an array ofdevices for forming differently sized or shaped countersinkscorresponding to the different proximal anchors.

As described above, in one embodiment, the proximal anchor 50 isconfigured such that it can be removed after being coupled and advanceover the body 28. In this manner, if the clinician determines afteradvancing the proximal anchor that the proximal anchor 50 is not of theright or most appropriate configuration (e.g., size and/or shape), theclinician can remove the proximal anchor 50 and advance a differentproximal anchor 50 over the body 28. In such an embodiment, the proximalanchor 50 is preferably provided with one or more engagement structures(e.g., slots, hexes, recesses, protrusions, etc.) configured to engage arotational and/or gripping device (e.g., slots, hexes, recesses,protrusions, etc.). Thus, in some embodiments, the proximal anchor 50can be pulled and/or rotated such that the anchor 50 is removed from thebody 28.

FIGS. 17 and 18 illustrate an embodiment of a tool 500 that can be usedto insert a proximal anchor 50 that utilizes a locking ring 51 (asdescribed above) onto a body 28 of the device 12. In the illustratedembodiment, the tool 500 comprises an elongated body 502 having a distalend 504 and a proximal end 506. The proximal end 506 is provided with ahandle 508 for manipulating the tool 500. The distal end 504 of thedevice is generally tubular and is coupled to or otherwise attached to adistal sleeve 510. The distal sleeve defines a chamber 511, whichextends from the distal end 504 of the elongated body 502 to the distalend 513 of the sleeve 510. A guidewire lumen 512 extend through the tool500.

With particular reference to FIG. 18, a pin 516 is partially positionedwithin the chamber 511. The pin 516 includes an enlarged proximalportion 518, which is positioned in the chamber 511. The pin 516 alsoincludes an reduced diameter portion 520, which extends outside thechamber 511. A guidewire lumen 522 also extend through the pin 516 suchthat the entire tool 500 can be inserted over a guidewire. A biasingmember 524 is positioned between the distal end 504 of the tubularmember 502 the proximal end 518 of the pin 516. In this manner, the pin516 is biased to the position shown in FIG. 18. Advantageously, thedistal end 520 of the pin 516 has an outside diameter that is slightlylarger than the inner diameter of the locking ring 51 (see e.g., FIG.10). Accordingly, the distal end 520 of the pin 516 can be inserted intothe proximal anchor through its proximal end. In one embodiment, thelocking ring 51 grasps the distal end 520 of the pin 516 to couple theproximal anchor 50 to the pin 516. In the loaded position, the proximalend of the proximal anchor 50 preferably contacts the distal end 513 ofthe distal sleeve 510.

In use, the tool 500 is coupled to the proximal anchor as describedabove. After the body 28 is inserted into the vertebrae. The tool 500 isused to position the proximal anchor 50 over the proximal end of thebody 28. The tool 500 is then advanced forward. As the tool 500 isadvanced forward, the proximal anchor 50 is pushed onto the body 28 asthe pin 516 retracts into the chamber 511. In this manner, the pin 516holds the locking ring 51 in an expanded position until it engages thebody 28. Once the pin 516 is fully retracted into the chamber 511, thepin 516 is decoupled from the proximal anchor 50 and the proximal anchor50 is fully coupled to the body 28.

In another embodiment, a dimension of the proximal anchor is capable ofbeing adjusted. For example, FIG. 19 illustrates an embodiment of aproximal anchor 700 in which the proximal anchor 700 can be radiallyexpanded such that the relationship between the anchor 700 and theadjacent vertebrae can be adjusted by the surgeon. In this embodiment,the anchor 700 comprises an wall 702, which can be formed of an elasticmaterial. The wall is coupled to an inner member 704 that comprises atubular housing 706 and a proximal flange 708, which can be arranged asdescribed above with reference to FIG. 10B. The wall 702 and the innermember 704 define a cavity 710, which can be filled with an inflationmaterial 712, such as, for example, a gas, liquid, gel, and/orhardenable or semi-hardenable media (e.g., an polymer, epoxy or cement).One or more valves 714 (e.g., a duck bill valve) can be provided alongthe wall 702. An inflation lumen 716 can extend through the valve suchthat the cavity 710 can be inflated with the inflation material 712.After inflation, the lumen 716 is removed and the valve 714 seals thecavity 710. One or more dividing walls 718 can be provided with thecavity 710 such that the anchor 50 can be inflated in discrete orsemi-discrete sections.

In one embodiment of use, the body 28 and proximal anchor 700 areinserted into position as described herein. The cavity 710 is theninflated to expand the proximal anchor 50 and increases its diameter. Inthis manner, the surgeon can control the degree to which the proximalanchor 50 limits the motion of the spine. For example, in oneembodiment, increasing the diameter of the proximal anchor 50 wouldincrease the distance between the two vertebrae. In some embodiments,the inflation material 712 can also be removed such that the dimensionscan be decreased during the same procedure in which the device 12 isinserted into the spine. In still other embodiments, the inflationmaterial 712 can be added or removed in a subsequent, preferably,minimally invasive second procedure such that the degree which theproximal anchor 50 limits the motion of the spine can be adjusted in thesecond, subsequent procedure. In one embodiment, this is done byinserting a lumen through the valve and adding and/or removing theinflation media 712.

FIGS. 20A-D illustrates another embodiment of a proximal anchor 750 inwhich one or more dimensions of the anchor 750 an be adjusted. In thisembodiment, the dimensions are adjusted using a mechanical mechanism.With reference to the illustrated embodiment, the anchor 750 can includea proximal member 752 and a distal member 754, which can be moveablycarried by the body 28 as described below. The proximal member 752defines a proximal stop 756 and the distal member 754 defines a distalstop 758. An expandable member 760 is positioned between the proximaland distal stops 756, 758. The expandable member 760 is configured toexpand radially as the proximal and distal stops 756, 758 are movedtowards each other and the expandable member 760 is compressedtherebetween. In one embodiment, the expandable member 760 comprises anelastic material that when compressed expands as shown in FIGS. 20A and20B. In another embodiment, the expandable member 760 comprises amalleable material (e.g., a metal or metal alloy) that is provided withone or more slots. In such an embodiment, the slots allow the member 760to expand as it is compressed between the proximal and distal stops 756,758.

With reference to FIG. 20D, the proximal member 752 can be provided witha recess 55 and ring 51 as described above with reference to FIGS. 5 and6. In this manner, the proximal member 752 can be advanced in the distaldirection while proximal movement of the member 752 is resisted. Ofcourse, other complementary retention structures can be used between themember 752 and the body 28 as described to permit distal movement whileresisting proximal movement. The distal movement of the distal member754 can be prevented by a distal stop 762 provided on the body 28. Asshown in FIG. 20D, the distal member 754 can be provided with a smoothbore 764 such that it can be advanced over the body 28 towards thedistal stop 762.

FIG. 21 illustrates an embodiment of a proximal anchor 770 which issimilar to the previous embodiment. In this embodiment, the proximalmember 752 includes threads 772 such that the proximal member 752 can bedistally advanced or proximal retracted by rotation. FIG. 22 illustratesanother embodiment of a proximal anchor 780. In this embodiment, theproximal member 752 is configured as described with reference FIG. 20D.However, the distal member 754 is provided with threads 782 such thatthe position of the distal member 754 on the body 28 can be adjusted.

The above described devices and techniques limit motion of the spine byproviding an abutment or wedge surface on one vertebrae or bodystructure. The abutment surface contacts, abuts, and/or wedges against aportion of a second, adjacent vertebrae or body structure so as limitleast one degree of motion between the two vertebra or body structurewhile permitting at least one other degree of motion. While the abovedescribed devices and techniques are generally preferred, certainfeatures and aspects can be extended to modified embodiments forlimiting motion between vertebra. These modified embodiments will now bedescribed.

In one embodiment, the proximal anchor 50 of the fixation device may be,coupled to, attached or integrally formed with the body 28. In thismanner, movement between the proximal anchor 50 and the body 28 is notpermitted. Instead, the clinician may chose a fixation device of theproper length and advance the device into the vertebrae until theproximal anchor lies flush with the vertebrae or is otherwise positionedaccordingly with respect to the vertebrae. In one particular,embodiment, the proximal anchor that is coupled to, attached orintegrally formed with the body 28 is configured to have an outersurface which can rotate, preferably freely, with respect to the body28. This arrangement advantageously reduces the tendency of the deviceto rotate and/or move within the inferior vertebrae as the proximalanchor 50 contacts the superior vertebrae.

In another embodiment, the abutment surface may be attached to thevertebrae through the use of an adhesive, fasteners, staples, screws andthe like. In still another embodiment, the abutment surface may formedon a distal end of a stabilization device that is inserted through thefront side of the vertebrae.

In the embodiments described above, the device 12 is generally insertedinto the spine from a posterior position such that a distal end of thedevice 12 is inserted into the first, inferior vertebrae and a proximalend of the device 12 contacts or wedges against the second, superiorvertebrae. However, it is anticipated that certain features and aspectsof the embodiments described herein can be applied to a procedure inwhich the device is inserted from a lateral or anterior site. In such anembodiment, the distal end or side portion of the device may contact orwedge against the second superior vertebrae. Such embodiments provide acontact or wedge surface which is supported by one body structure tolimit of the motion of an adjacent body structure.

In the embodiments, described above, it is generally advantageous thatthe proximal anchor be radiopaque or otherwise configured such that incan be seen with visual aids used during surgery. In this manner, thesurgeon can more accurately position the proximal anchor with respect tothe superior and inferior vertebra.

Preferably, the clinician will have access to an array of fixationdevices 12, having, for example, different diameters, axial lengths and,if applicable, angular relationships. These may be packaged one or moreper package in sterile or non-sterile envelopes or peelable pouches, orin dispensing cartridges which may each hold a plurality of devices 12.The clinician will assess the dimensions and load requirements, andselect a fixation device from the array, which meets the desiredspecifications.

The fixation devices may also be made from conventional non-absorbable,biocompatible materials including stainless steel, titanium, alloysthereof, polymers, composites and the like and equivalents thereof. Inone embodiment, the distal anchor comprises a metal helix, while thebody and the proximal anchor comprise a bioabsorbable material. Inanother embodiment, the body is made of PEEK™ polymer or similar plasticmaterial. Alternatively, the distal anchor comprises a bioabsorbablematerial, and the body and proximal anchor comprise either abioabsorbable material or a non-absorbable material. As a furtheralternative, each of the distal anchor and the body comprise anon-absorbable material, connected by an absorbable link. This may beaccomplished by providing a concentric fit between the distal anchor andthe body, with a transverse absorbable pin extending therethrough. Thisembodiment will enable removal of the body following dissipation of thepin, while leaving the distal anchor within the bone.

The components of the present invention may be sterilized by any of thewell known sterilization techniques, depending on the type of material.Suitable sterilization techniques include, but not limited to heatsterilization, radiation sterilization, such as cobalt 60 irradiation orelectron beams, ethylene oxide sterilization, and the like.

The specific dimensions of any of the bone fixation devices of thepresent invention can be readily varied depending upon the intendedapplication, as will be apparent to those of skill in the art in view ofthe disclosure herein. Moreover, although the present invention has beendescribed in terms of certain preferred embodiments, other embodimentsof the invention including variations in dimensions, configuration andmaterials will be apparent to those of skill in the art in view of thedisclosure herein. In addition, all features discussed in connectionwith any one embodiment herein can be readily adapted for use in otherembodiments herein. The use of different terms or reference numerals forsimilar features in different embodiments does not imply differencesother than those which may be expressly set forth. Accordingly, thepresent invention is intended to be described solely by reference to theappended claims, and not limited to the preferred embodiments disclosedherein.

What is claimed is:
 1. A method of using a spinal stabilization devicecomprising: coupling a distal anchor of an elongate body of the spinalstabilization device into a patient, the elongate body having alongitudinal axis extending from a proximal end of the elongate body toa distal end of the distal anchor; advancing a proximal anchor of thestabilization device from the proximal end of the elongate body and overthe elongate body toward the distal end of the distal anchor, whereinthe proximal anchor is advanced along the longitudinal axis of theelongate body, wherein the proximal anchor is advanced along a threadedsurface of the elongate body; and selectively inflating the proximalanchor after the proximal anchor is coupled to the elongate body.
 2. Themethod of claim 1, wherein selectively inflating the proximal anchorfurther comprises selectively inflating a cavity of the proximal anchor.3. The method of claim 2, further comprising sealing the cavity.
 4. Themethod of claim 2, wherein selectively inflating the proximal anchorfurther comprises adding an inflation material to the cavity.
 5. Themethod of claim 4, wherein the inflation material comprises at least onematerial from a group consisting of a gas, liquid, gel and hardenablemedia.
 6. The method of claim 1, wherein selectively inflating theproximal anchor further comprises radially expanding the proximalanchor.
 7. The method of claim 1, wherein selectively inflating theproximal anchor further comprises adjusting the relationship between thespinal stabilization device and an adjacent vertebrae.
 8. The method ofclaim 1, wherein selectively inflating the proximal anchor furthercomprises expanding a wall formed of an elastic material.
 9. The methodof claim 1, wherein selectively inflating the proximal anchor furthercomprises using one or more valve.
 10. The method of claim 1, furthercomprising increasing the distance between two vertebrae by increasingthe diameter of the proximal anchor.
 11. A method of using a spinalstabilization device comprising: coupling a distal anchor of an elongatebody of the spinal stabilization device into a patient, the elongatebody comprising a longitudinal axis from a proximal end of the elongatebody to a distal end of the distal anchor; advancing a proximal anchorof the stabilization device over the elongate body from the proximal endof the elongate body and along the longitudinal axis toward the distalend the distal anchor, wherein the proximal anchor is advanced along athreaded surface of the elongate body; and selectively deflating theproximal anchor after the proximal anchor is coupled to the elongatebody.
 12. The method of claim 11, wherein selectively deflating theproximal anchor further comprises selectively deflating a cavity of theproximal anchor.
 13. The method of claim 12, further comprising sealingthe cavity.
 14. The method of claim 12, wherein selectively deflatingthe proximal anchor further comprises removing an inflation materialfrom the cavity.
 15. The method of claim 14, wherein the inflationmaterial comprises at least one material from a group consisting of agas, liquid, gel and hardenable media.
 16. The method of claim 11,wherein selectively deflating the proximal anchor further comprisesradially contracting the proximal anchor.
 17. The method of claim 11,wherein selectively deflating the proximal anchor further comprisesadjusting the relationship between the spinal stabilization device andan adjacent vertebrae.
 18. The method of claim 11, wherein selectivelydeflating the proximal anchor further comprises contracting a wallformed of an elastic material.
 19. The method of claim 11, whereinselectively deflating the proximal anchor further comprises using one ormore valve.
 20. The method of claim 11, further comprising decreasingthe distance between two vertebrae by decreasing the diameter of theproximal anchor.